U.S. Pat. No. 6,573,030, which is incorporated herein by reference, has disclosed a process in which a mask comprising two mask layers is applied to a substrate. The first mask layer is a carbon-containing layer that is formed as part of a deposition process using a gas containing carbon and hydrogen. A second mask layer, which may consist, for example, of an oxide, a nitride, a silicon oxynitride, a silicon carbide, amorphous silicon or other materials, is applied to this carbon-containing mask layer. The two mask layers are patterned using a photoresist mask, so as to form the finished, patterned mask. The finished mask can be used, for example, to etch substrate structures, i.e., structures in or on the substrate.
The document “Generating Sub-30 nm Poly-Silicon Gates Using PECVD Amorphous Carbon as Hardmask and Anti-Reflective Coating” (Wei Liu Mui, Thorsten Lill, May Wang, Chris Bencher, Michael Kwan and Wendy Yeh; Proceedings SPIE, 2003; 5040(1): 841-8.), incorporated herein by reference, has likewise disclosed a process in which a carbon-containing mask layer is patterned as a mask and then used further. It is stated in this document that the feature size of the structures of the carbon-containing mask layer can subsequently be reduced by an additional “trimming” step until predetermined desired dimensions are reached.